Ammonium perchlorate is a well known oxidizer for solid rocket propellants. One commonly employed technique for changing the burning rate of a solid rocket propellant is to change the particle size of the ammonium perchlorate oxidizer. In general, the burning rate increases as the average particle size of the oxidizer decreases. The comminution of ammonium perchlorate has been most commonly accomplished by various grinding techniques. More recently, the increased demand for very fast burning propellants has increased the search for a practical process of producing even finer ammonium perchlorate particles, that is, particles having an average particle diameter of less than 6 microns. Such a process to be practical must be capable of providing suitably large quantities of the very fine ammonium perchlorate on a reproducible basis. One problem which has plagued efforts to produce the very fine ammonium perchlorate particles has been the tendency of the finely divided material to re-grow or agglomerate during the manufacturing process or in storage, forming a coarser or lumpy product which is unacceptable and does not achieve the desired increase in burning rate. The fundamental causes underlying re-growth or agglomeration have not been precisely established but it appears that the phenomenon occurs primarily due to deliquescence, recrystallization, electrical, or pressure effects. For this reason various coating techniques have been suggested to reduce the tendency of the finely divided ammonium perchlorate particles to undergo re-growth or agglomeration. For example, silicon-containing materials such as Cab-O-Sil, magnesium oxide, magnesium stearate, calcium phosphate, various fatty acid amine derivatives and certain dyes have been applied both before and after the grinding of the ammonium perchlorate to prevent re-growth and agglomeration. However, none of these techniques have been entirely successful in solving the problem in the present invention. It is believed for the first there has been provided a way of producing finely divided ammonium perchlorate oxidizer on a reproducible basis which does not undergo re-growth or agglomeration.